A HYBRID THREE-SCALE MODEL OF TUMOR GROWTH.

Cancer results from a complex interplay of different biological, chemical, and physical phenomena that span a wide range of time and length scales. Computational modeling may help to unfold the role of multiple evolving factors that exist and interact in the tumor microenvironment. Understanding these complex multiscale interactions is a crucial step towards predicting cancer growth and in developing effective therapies. We integrate different modeling approaches in a multiscale, avascular, hybrid tumor growth model encompassing tissue, cell, and sub-cell scales. At the tissue level, we consider the dispersion of nutrients and growth factors in the tumor microenvironment, which are modeled through reaction-diffusion equations. At the cell level, we use an agent based model (ABM) to describe normal and tumor cell dynamics, with normal cells kept in homeostasis and cancer cells differentiated apoptotic, hypoxic, and necrotic states. Cell movement is driven by the balance of a variety of forces according to Newton's second law, including those related to growth-induced stresses. Phenotypic transitions are defined by specific rule of behaviors that depend on microenvironment stimuli. We integrate in each cell/agent a branch of the epidermal growth factor receptor (EGFR) pathway. This pathway is modeled by a system of coupled nonlinear differential equations involving the mass laws of 20 molecules. The rates of change in the concentration of some key molecules trigger proliferation or migration advantage response. The bridge between cell and tissue scales is built through the reaction and source terms of the partial differential equations. Our hybrid model is built in a modular way, enabling the investigation of the role of different mechanisms at multiple scales on tumor progression. This strategy allows representating both the collective behavior due to cell assembly as well as microscopic intracellular phenomena described by signal transduction pathways. Here, we investigate the impact of some mechanisms associated with sustained proliferation on cancer progression. Specifically, we focus on the intracellular proliferation/migration-advantage-response driven by the EGFR pathway and on proliferation inhibition due to accumulation of growth-induced stresses. Simulations demonstrate that the model can adequately describe some complex mechanisms of tumor dynamics, including growth arrest in avascular tumors. Both the sub-cell model and growth-induced stresses give rise to heterogeneity in the tumor expansion and a rich variety of tumor behaviors.

Prenatal hypoxia, habituation memory and oxidative stress.

Hypoxia-ischemia (HI) is characterized by a reduced supply of oxygen during pregnancy, which leads to both central nervous system and peripheral injuries in the foetus, resulting in impairment in its development. The purpose of this study was to investigate behavioural changes and systemic oxidative stress in adult animals that have been affected by HI during pregnancy. HI was induced by the occlusion of the maternal uterine artery with aneurysm clamps for a period of 45 min on the 18th gestational day. Animals from the sham group were submitted to same surgical procedure as the HI animals, without occlusion of the maternal uterine artery. The control group consisted of non-manipulated healthy animals. At postnatal day 90, the pups were submitted to behavioural tests followed by blood collection. HI adult animals presented an increase in anxiety behaviour and a lack of habituation compared to both sham and control groups. Oxidative damage, assessed by protein and lipid oxidation in serum, did not differ between HI and sham-operated animals. However, HI animals presented reduced activity of the glutathione peroxidase enzyme and increased formation of nitrite, indicating alterations in the systemic antioxidant repair system. Our results suggest an association among HI, systemic oxidative stress and behavioural alterations.

Effect of propofol on human fetal placental circulation.

BACKGROUND: Propofol is an alternative to thiopental for induction of general anaesthesia for cesarean section. It crosses the placenta and induces vasodilatation of isolated vessels and may therefore alter fetal placental vascular resistance. The direct effect of propofol on the fetal placental circulation was studied in vitro. The actions of propofol on vasoconstrictive effects induced by angiotensin II (Ang II), bradykinin (BK), prostaglandin F(2alpha) (PGF(2alpha)) and potassium chloride (KCl) were evaluated. METHODS: Full-term healthy human placentas (n=48) were perfused with modified Tyrode's solution using a pulsatile pump. Placental perfusion pressure was measured in response to injection of Ang II, BK, KCl and PGF(2alpha) before and after perfusion with propofol (1.7 x 10(-5) and 5.6 x 10(-5) M). RESULTS: BK, Ang II, KCl and PGF(2alpha) induced a dose-dependent increase in placental perfusion pressure. Propofol induced a concentration-dependent decrease in placental perfusion pressure, but this was not observed with the propofol solvent (Intralipid). Propofol, but not Intralipid, reduced the vasoconstrictor effects of BK, KCl and PGF(2alpha), while the effect of Ang II was not changed. The effect of KCl was abolished in placentas perfused with Ca(2+)-free solution, while the effect of Ang II was not altered. CONCLUSIONS: Propofol induced vasodilatation and inhibited the vasoconstrictive effects of BK and PGF(2alpha), in the human placenta. These findings suggest that propofol may not reduce fetal placental blood flow. Since propofol reduced the vasoconstricting effect of KCl but not that of AngII, we propose that the vasodilatory effect of propofol in the human placenta involves inhibition of Ca(2+) channels.

Acquisition and cross-transmission of Staphylococcus aureus in European intensive care units.

OBJECTIVE: To study the acquisition and cross-transmission of Staphylococcus aureus in different intensive care units (ICUs). METHODS: We performed a multicenter cohort study. Six ICUs in 6 countries participated. During a 3-month period at each ICU, all patients had nasal and perineal swab specimens obtained at ICU admission and during their stay. All S. aureus isolates that were collected were genotyped by spa typing and multilocus variable-number tandem-repeat analysis typing for cross-transmission analysis. A total of 629 patients were admitted to ICUs, and 224 of these patients were found to be colonized with S. aureus at least once during ICU stay (22% were found to be colonized with methicillin-resistant S. aureus [MRSA]). A total of 316 patients who had test results negative for S. aureus at ICU admission and had at least 1 follow-up swab sample obtained for culture were eligible for acquisition analysis. RESULTS: A total of 45 patients acquired S. aureus during ICU stay (31 acquired methicillin-susceptible S. aureus [MSSA], and 14 acquired MRSA). Several factors that were believed to affect the rate of acquisition of S. aureus were analyzed in univariate and multivariate analyses, including the amount of hand disinfectant used, colonization pressure, number of beds per nurse, antibiotic use, length of stay, and ICU setting (private room versus open ICU treatment). Greater colonization pressure and a greater number of beds per nurse correlated with a higher rate of acquisition for both MSSA and MRSA. The type of ICU setting was related to MRSA acquisition only, and the amount of hand disinfectant used was related to MSSA acquisition only. In 18 (40%) of the cases of S. aureus acquisition, cross-transmission from another patient was possible. CONCLUSIONS: Colonization pressure, the number of beds per nurse, and the treatment of all patients in private rooms correlated with the number of S. aureus acquisitions on an ICU. The amount of hand disinfectant used was correlated with the number of cases of MSSA acquisition but not with the number of cases of MRSA acquisition. The number of cases of patient-to-patient cross-transmission was comparable for MSSA and MRSA.

Angiotensin II-mediated vasodilation is reduced in adult spontaneously hypertensive rats despite enhanced expression of AT2 receptors.

1. The vasodilator action of angiotensin (Ang) II has not yet been demonstrated in spontaneously hypertensive rats (SHR), nor have any possible changes in this response during the development of hypertension. 2. In the present study, the vasodilator effect of AngII was evaluated in the rat isolated, preconstricted mesenteric arterial bed (MAB) from 6- (young) and 24-week-old (adult) SHR and compared with effects on MAB from age-matched normotensive rats (control). 3. Angiotensin II (10-300 nmol) induced vasodilation in noradrenaline (NA)-preconstricted MAB that was greater in vessels from young compared with adult rats in both the control and SHR groups. Angiotensin II-induced vasodilation was reduced by the angiotensin AT(2) receptor antagonist PD 123319 (10 micromol/L), the angiotensin-(1-7) receptor antagonist A779 (1 micromol/L) and the bradykinin B(2) receptor antagonist HOE-140 (0.01 micromol/L), but not by the AT(1) receptor antagonist losartan (30 micromol/L). Expression of AT(2) receptors was weak in vessels from adult control rats compared with that in young control rats, whereas in young SHR AT(2) receptor expression was increased compared with that in young control rats. This increased expression of AT(2) receptors was maintained in adult SHR and there was no significant difference in AT(2) receptor expression between young and old SHR. 4. The findings of the present suggest that AngII induces an AT(2) receptor-mediated vasodilator effect in the MAB via activation of angiotensin-(1-7) and bradykinin receptors, an action that is reduced in adult control rats and adult SHR. In adult control rats, the attenuated response of AngII is probably due to endothelial dysfunction and reduced expression of AT(2) receptors, whereas in adult SHR it is associated with endothelial dysfunction alone. Increased expression of AT(2) receptors in SHR may represent a counteracting response for modulating blood pressure.

The role of NO-cGMP pathway and potassium channels on the relaxation induced by clonidine in the rat mesenteric arterial bed.

The mechanisms involved in the vasodilation action of clonidine have not yet been completely elucidated. We investigated the potential mechanisms that seem to be involved in the clonidine vasodilator effect using rat isolated mesenteric arterial bed (MAB). In precontracted MAB, clonidine (10-300 pmol) induced a dose-dependent relaxation, that was inhibited by endothelium removal (deoxycholic acid - 2.5 mM) and reduced by the alpha(2) adrenoceptor inhibitors yohimbine (1-3 microM) and rauwolscine (1 microM). The endothelium-dependent vasodilation induced by clonidine was reduced by the nitric oxide (NO) synthase inhibitor L-NAME (0.3 mM) and guanylyl cyclase inhibitor ODQ (10 microM) but was not affected by indomethacin (3-10 microM) alone. High K+ (25 mM) solution reduced the vasodilator effect of clonidine that was further attenuated by L-NAME. In the presence of high K+ plus L-NAME, the residual vasodilator effect of clonidine was further reduced by indomethacin (3 microM). The Ca(2+)-dependent K+ channel (K+(Ca2+)) inhibitors, charybdotoxin (ChTx; 0.1 microM) plus apamin (0.1 microM), also reduced the vasodilation induced by clonidine, however this response was not further reduced in the presence of L-NAME as observed with acetylcholine (10 pmol). In the presence of ATP-dependent K+ channel (K+(ATP)) blocker, glibenclamide (10 microM), the inhibitory effect of ChTx plus apamin plus L-NAME was increased. In contrast, the vasodilation induced by clonidine was not affected by voltage-dependent K+ channels (K(V)) blocker, 4-aminopyridine (4-AP, 1 mM). In conclusion, our results demonstrate that clonidine activates alpha(2)-adrenoceptors in rat MAB and that the endothelium-dependent vasodilation is mediated by activation of NO-cGMP pathway, hyperpolarization due to activation of K+(Ca) and K+(ATP) channels. Prostaglandins might participate in the vasodilator effect of clonidine when NO and EDHF mechanisms are blunted.

Endothelium-dependent vasodilator effect of Euterpe oleracea Mart. (Açaí) extracts in mesenteric vascular bed of the rat.

Açai (Euterpe oleracea Mart.) a fruit from the Amazon region, largely consumed in Brazil is rich in polyphenols. Experiments were undertaken to determine whether hydro-alcoholic extract obtained from stone of açaí induces a vasodilator effect in the rat mesenteric vascular bed precontracted with norepinephrine (NE) and, if so, to elucidate the underlying mechanism. Açai stone extract (ASE, 0.3-100 microg) induced a long-lasting endothelium-dependent vasodilation that was significantly reduced by N(G)-nitro-l-arginine methyl ester (l-NAME) and (1)H-[1,2,3] oxadiazolo [4,4-a] quinoxalin-l-one (ODQ) and abolished by KCl (45 mM) plus l-NAME. In vessels precontrated with NE and KCl (45 mM) or treated with K(Ca)(+2) channel blockers (charybdotoxin plus apamin), the effect of ASE was significantly reduced. However this effect is not affect by indomethacin, glybenclamide and 4-aminopiridine. Atropine, pyrilamine, yohimbine and HOE 140 significantly reduced the vasodilator effect of acetylcholine, histamine, clonidine and bradykinin, respectively, but did not change the vasodilator effect of ASE. In cultured endothelial cells ASE (100 microg/mL) induced the formation of NO that was reduced by N(G)-nitro-l-arginine (l-NA, 100 microM). The present study demonstrates that the vasodilator effect of ASE is dependent on activation of NO-cGMP pathway and may also involve endothelium-derived hyperpolarizing factor (EDHF) release. The vasodilator effect suggest a possibility to use ASE as a medicinal plant, in the treatment of cardiovascular diseases.

Antihypertensive and endothelium-dependent vasodilator effects of Alpinia zerumbet, a medicinal plant.

Alpinia zerumbet (K. Schum), a medicinal plant originated from West Asia, is used in the northeast and southeast of Brazil as infusions or decoctions as a diuretic, antihypertensive, and antiulcerogenic. Experiments were undertaken to determine whether a hydroalcoholic extract obtained from leaves of Alpinia zerumbet (AZE) induces vasodilation in the mesenteric vascular bed (MVB), and an antihypertensive effect was also assessed in rats with DOCA-salt hypertension. In MVB precontracted with norepinephrine, AZE induces a long-lasting endothelium-dependent vasodilation that is not reduced by indomethacin. Inhibition of NO synthase by NG-nitro-L-arginine methyl ester (L-NAME) and guanylyl cyclase by 1H-[1,2,3]oxadiazolo [4,4-a]quinoxalin-1-one (ODQ) reduces the vasodilator effect of AZE. In vessels precontracted with norepinephrine, the vasodilator effect of AZE was not changed by 4-aminopyridine, glibenclamide, or by charybdotoxin plus apamin. Concentrations of atropine, pyrilamine, and yohimbine that significantly reduced the vasodilator effect of acetylcholine, histamine, and clonidine, respectively, did not change the vasodilator effect of AZE. HOE 140, which significantly reduced the vasodilator effect of bradykinin, induced a slight but significant reduction on the vasodilator effect of AZE. Chronic oral administration of AZE induced a significant reduction in systolic, mean, and diastolic arterial pressure in rats with DOCA-salt hypertension. Probably the vasodilator effect of AZE is dependent on the activation of the NO-cGMP pathway and independent of activation of ATP-dependent, voltage-dependent, and calcium-dependent K+ channels. Bradykinin receptors may also participate in the vasodilator effect of AZE. Finally, the vasodilator and antihypertensive effects of AZE demonstrated in the present study provide experimental support for the indication of Alpinia zerumbet as an antihypertensive medicinal plant.

Captopril reverses the reduced vasodilator response to bradykinin in hypertensive pregnant rats.

1. Pregnancy in rats is characterized by a reduction in arterial pressure that is associated with a decreased response to vasoconstrictors. However, the responses to vasodilators in isolated vessels remain controversial and are not well established in hypertensive pregnant rats. 2. In the present study, we investigated the effect of pregnancy on the bradykinin (BK)-induced vasodilator responses of the isolated mesenteric arterial bed (MAB) from Wistar normotensive and spontaneously hypertensive rats (SHR) and determined the role of nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF) and angiotensin-converting enzyme (ACE) in these responses. 3. Mean arterial pressure (MAP) in pregnant normotensive and pregnant hypertensive rats (93 +/- 1 and 122 +/- 2 mmHg, respectively) was lower than in non-pregnant controls (128 +/- 1 and 163 +/- 2 mmHg, respectively; P < 0.05). In MAB isolated from normotensive rats and precontracted with phenylephrine, the effects of bradykinin, acetylcholine (ACh) and nitroglycerine (NG) were not influenced by pregnancy. In contrast, the vasodilator responses to BK were significantly reduced in pregnant compared with non-pregnant SHR and seemed to be specific to BK. 4. The ACE inhibitor captopril potentiated BK vasodilator responses and abolished the differences between pregnant and non-pregnant SHR. Inhibition of nitric oxide (NO) synthase by N(G)-nitro-L-arginine methyl ester (l-NAME) significantly reduced the vasodilator effect of BK in all groups. In the presence of l-NAME plus high K+ solution (47 mmol/L), BK-induced vasodilation was completely blocked. The NO-dependent component of the responses seems to be more important in hypertensive rats and pregnancy does not modify this profile. 5. Our results suggest that increased ACE activity may be involved in the pregnancy associated reduction in vasodilator responses to BK in the MAB of hypertensive rats. Pregnancy does not modify the relative contribution of the EDHF and NO to the vasodilator effect of BK.

The role of bradykinin, AT2 and angiotensin 1-7 receptors in the EDRF-dependent vasodilator effect of angiotensin II on the isolated mesenteric vascular bed of the rat.

1. The mechanisms involved in the vasodilator actions of angiotensin II (Ang II) have not yet been completely elucidated. We investigated the potential mechanisms that seem to be involved in the Ang II vasodilator effect using rat isolated mesenteric vascular bed (MVB). 2. Under basal conditions, Ang II does not affect the perfusion pressure of MVB. However, in vessels precontracted with norepinephrine, Ang II induces vasodilation followed by vasoconstriction. Vasoconstrictor, but not the vasodilation of Ang II, is inhibited by AT(1) antagonist (losartan). The vasodilator effect of Ang II was not inhibited by AT(2), angiotensin IV and angiotensin 1-7 receptor antagonists alone (PD 123319, divalinal, A 779, respectively). 3. The vasodilator effect of Ang II is significantly reduced by endothelial removal (deoxycholic acid), but not by indomethacin. Inhibition of NO-synthase by N(G)-nitro-l-arginine methyl ester (l-NAME) and guanylyl cyclase by 1H-[1,2,3] oxadiazolo [4,4-a] quinoxalin-1-one (ODQ) reduces the vasodilator effect of Ang II. This effect is also reduced by tetraethylammonium (TEA) or l-NAME, and a combination of l-NAME plus TEA increases the inhibitory effect of the antagonists alone. However, indomethacin does not change the residual vasodilator effect observed in vessels pretreated with l-NAME plus TEA. 4. In vessels precontracted with norepinephrine and depolarized with KCl 25 mm or treated with Ca(2+)-dependent K(+) channel blockers (charybdotoxin plus apamin), the effect of Ang II was significantly reduced. However, this effect is not affected by ATP and voltage-dependent K(+) channel blockers (glybenclamide and 4-aminopyridine). 5. Inhibition of kininase II with captopril significantly potentiates the vasodilator effect of bradykinin (BK) and Ang II in the rat MVB. The inhibitory effect of the B(2) receptor antagonist HOE 140 on the vasodilator effect of Ang II is further enhanced by PD 123319 and/or A 779. 6. The present findings suggest that BK plays an important role in the endothelium-dependent vasodilator effect of Ang II. Probably, the link between Ang II and BK release is modulated by receptors that bind PD 123319 and A 779.

The effects of nitric oxide synthase inhibitors on the sedative effect of clonidine.

UNLABELLED: The mechanism underlying the Niteroi, Rio de Janeiro sedative effect of clonidine, an alpha2-adrenoceptor agonist, remains uncertain. Because activation of alpha2-adrenoceptors induces release of nitric oxide (NO), we tested the hypothesis that the sedative effect of clonidine depends on NO-related mechanisms. The effect of 7-nitro indazole on the sleeping time induced by clonidine was studied in Wistar rats. In addition, we examined the effect of clonidine, alpha-methyldopa, and midazolam on the thiopental-induced sleeping time in rats pretreated with N(G)-nitro-L-arginine-methyl-ester (L-NAME). The sleeping time induced by clonidine was significantly decreased by 7-nitro indazole. Thiopental sleeping time was increased by clonidine, alpha-methyldopa, and midazolam. L-NAME reduced the prolongation effect of clonidine and alpha-methyldopa, but did not alter the effect of midazolam on the thiopental-induced sleeping time. The inhibitory effect of L-NAME on clonidine-dependent prolongation of thiopental-induced sleeping time was reversed by L-arginine. These results suggest that NO-dependent mechanisms are involved in the sedative effect of clonidine. In addition, this effect seems to be specific for the sedative action of alpha2-adrenoceptors agonists. IMPLICATIONS: Clonidine, an antihypertensive drug, is also a sedative. This sedative effect, although an adverse event in the treatment of hypertensive patients, can be helpful for sedation of surgical patients. The mechanism of this effect, however, is unknown. In this study, we show that the sedative effect of clonidine is mediated by nitric oxide, because it could be prevented by pretreatment with nitric oxide synthase inhibitors.

Actions of L-NAME and methylene blue on the hypotensive effects of clonidine and rilmenidine in the anesthetized rat.

The antihypertensive mechanism of alpha2-adrenoceptor agonists, such as clonidine and rilmenidine, is not completely elucidated, although it is probably due to reduction of sympathetic tone mediated by stimulation of central alpha2-adrenoceptors. Because activation of alpha2-adrenoceptors on endothelial cells induces release of endothelium-derived relaxing factor (EDRF), we determined whether nitric oxide (NO) release is involved in the antihypertensive action of clonidine and rilmenidine. In chloralose-anesthetised Wistar rats, systolic and diastolic arterial blood pressures were recorded on a polygraph. Intravenous injection of clonidine or rilmenidine (control group) caused a rapid increase of arterial blood pressure. followed by a long-lasting hypotensive effect. The hypotensive effects, estimated as the area enclosed by the decrease in diastolic pressure during the 20 min after clonidine and rilmenidine injections, were 574+/-60 and 410+/-59 mm Hg/min, respectively. The delta decrease in diastolic arterial blood pressure observed 20 min after intravenous injections of clonidine and rilmenidine was 48+/-5 and 34+/-3 mm Hg, respectively. Clonidine and rilmenidine injected 5-10 min after intravenous pretreatment with L-NAME (2 and 1 mg/kg) or methylene blue (10 mg/kg) induced hypotensive effects that were significantly smaller than that observed for the control group. These results suggest that the antihypertensive effects of clonidine and rilmenidine also may be modulated by the NO-cyclic guanosine monophosphate (cGMP) pathway at the level of the central nervous system and/or at the vascular peripheral circulation.

Role of non-nitric oxide non-prostaglandin endothelium-derived relaxing factor(s) in bradykinin vasodilation

The most conspicuous effect of bradykinin following its administration into the systemic circulation is a transient hypotension due to vasodilation. In the present study most of the available evidence regarding the mechanisms involved in bradykinin-induced arterial vasodilation is reviewed. It has become firmly established that in most species vasodilation in response to bradykinin is mediated by the release of endothelial relaxing factors following the activation of B2-receptors. Although in some cases the action of bradykinin is entirely mediated by the endothelial release of nitric oxide (NO) and/or prostacyclin (PGI2), a large amount of evidence has been accumulated during the last 10 years indicating that a non-NO/PGI2 factor accounts for bradykinin-induced vasodilation in a wide variety of perfused vascular beds and isolated small arteries from several species including humans. Since the effect of the non-NO/PGI2 endothelium-derived relaxing factor is practically abolished by disrupting the K+ electrochemical gradient together with the fact that bradykinin causes endothelium-dependent hyperpolarization of vascular smooth muscle cells, the action of such factor has been attributed to the opening of K+ channels in these cells. The pharmacological characteristics of these channels are not uniform among the different blood vessels in which they have been examined. Although there is some evidence indicating a role for KCa or KV channels, our findings in the mesenteric bed together with other reports indicate that the K+ channels involved do not correspond exactly to any of those already described. In addition, the chemical identity of such hyperpolarizing factor is still a matter of controversy. The postulated main contenders are epoxyeicosatrienoic acids or endocannabinoid agonists for the CB1-receptors. Based on the available reports and on data from our laboratory in the rat mesenteric bed, we conclude that the NO/PGI2-independent endothelium-dependent vasodilation induced by BK is unlikely to involve a cytochrome P450 arachidonic acid metabolite or an endocannabinoid agonist.

Role of non-nitric oxide non-prostaglandin endothelium-derived relaxing factor(s) in bradykinin vasodilation.

The most conspicuous effect of bradykinin following its administration into the systemic circulation is a transient hypotension due to vasodilation. In the present study most of the available evidence regarding the mechanisms involved in bradykinin-induced arterial vasodilation is reviewed. It has become firmly established that in most species vasodilation in response to bradykinin is mediated by the release of endothelial relaxing factors following the activation of B2-receptors. Although in some cases the action of bradykinin is entirely mediated by the endothelial release of nitric oxide (NO) and/or prostacyclin (PGI2), a large amount of evidence has been accumulated during the last 10 years indicating that a non-NO/PGI2 factor accounts for bradykinin-induced vasodilation in a wide variety of perfused vascular beds and isolated small arteries from several species including humans. Since the effect of the non-NO/PGI2 endothelium-derived relaxing factor is practically abolished by disrupting the K+ electrochemical gradient together with the fact that bradykinin causes endothelium-dependent hyperpolarization of vascular smooth muscle cells, the action of such factor has been attributed to the opening of K+ channels in these cells. The pharmacological characteristics of these channels are not uniform among the different blood vessels in which they have been examined. Although there is some evidence indicating a role for KCa or KV channels, our findings in the mesenteric bed together with other reports indicate that the K+ channels involved do not correspond exactly to any of those already described. In addition, the chemical identity of such hyperpolarizing factor is still a matter of controversy. The postulated main contenders are epoxyeicosatrienoic acids or endocannabinoid agonists for the CB1-receptors. Based on the available reports and on data from our laboratory in the rat mesenteric bed, we conclude that the NO/PGI2-independent endothelium-dependent vasodilation induced by BK is unlikely to involve a cytochrome P450 arachidonic acid metabolite or an endocannabinoid agonist.

Role of endothelium in angiotensin II formation by the rat aorta and mesenteric arterial bed.

We investigated the angiotensin II (Ang II)-generating system by analyzing the vasoconstrictor effect of Ang II, angiotensin J (Ang I), and tetradecapeptide (TDP) renin substrate in the absence and presence of inhibitors of the renin-angiotensin system in isolated rat aortic rings and mesenteric arterial beds with and without functional endothelium. Ang II, Ang I, and TDP elicited a dose-dependent vasoconstrictor effect in both vascular preparations that was completely blocked by the Ang II receptor antagonist saralasin (50 nM). The angiotensin converting enzyme (ACE) inhibitor captopril (36 microM) completely inhibited the vasoconstrictor effect elicited by Ang I and TDP in aortic rings without affecting that of Ang II. In contrast, captopril (36 microM) significantly reduced (80-90%) the response to bolus injection of Ang I, without affecting those to Ang II and TDP in mesenteric arteries. Mechanical removal of the endothelium greatly potentiated (70-95%) the vasoconstrictor response to Ang II, Ang I, and TDP in aortic rings while these responses were unaffected by the removal of the endothelium of mesenteric arteries with sodium deoxycholate infusion. In addition, endothelium disruption did not change the pattern of response elicited by these peptides in the presence of captopril. These findings indicate that the endothelium may not be essential for Ang II formation in rat mesenteric arteries and aorta, but it may modulate the response to Ang II. Although Ang II formation from Ang I is essentially dependent on ACE in both vessels, our results suggest the existence of an alternative pathway in the mesenteric arterial bed that may play an important role in Ang II generation from TDP in resistance but not in large vessels during ACE inhibition.

Role of endothelium in angiotensin II formation by the rat aorta and mesenteric arterial bed

We investigated the angiotensin II (Ang II)-generating system by analyzing the vasoconstrictor effect of Ang II, angiotensin I (Ang I), and tetradecapeptide (TDP) renin substrate in the abscence and presence of inhibitors of the renin-angiotensin system in isolated rat aortic rings and mesenteric arterial beds with and without functional endothelium. Ang II, Ang I, and TDP elicited a dose-dependent vasoconstrictor effect in both vascular preparations that was completely blocked by the Ang II receptor antagonist saralasin (50 nM). The angiotensin converting enzyme (ACE) inhibitor captopril (36 muM) completely inhibited the vasoconstrictor effect elicited by Ang I and TDP in aortic rings without affecting that of Ang II. In contrast, captopril (36 muM) significantly reduced (80-90 percent) the response to bolus injection of Ang I, without affecting those to Ang II and TDP in mesenteric arteries. Mechanical removal of the endothelium greatly potentiated (70-95 percent) the vasoconstrictor response to Ang II, Ang I, and TDP in aortic rings while these responses were unaffected by the removal of the endothelium of mesenteric arteries with sodium deoxycholate infusion. In addition, endothelium disruption did not change the pattern of response elicited by these peptides in the presence of captopril. These findings indicate that the endothelium may not be essential for Ang II formation in rat mesenteric arteries and aorta, but it may modulate the response to Ang II. Although Ang II formation from Ang I is essentially dependent on ACE in both vessels, our results suggest the existence of an alternative pathway in the mesenteric arterial bed that may play an important role in Ang II generation from TDP in resistence but not in large vessels during ACE inhibition.

Determinaçäo da digestibilidade aparente em equídeos através do óxido crômico, da lignina e da coleta total das fezes / Apparent digestibility using total fecal collection, chromic oxide and lignin as markers in equids

Foram comparados os coeficientes de digestibilidade da proteína bruta (PB), matéria seca (MS), hemicelulose (HCEL), fibra em detergente neutro (FDN), fibra em detergente ácido (FDA), energia bruta (EB) e celulose (CEL), obtidos pela coleta total das fezes (CT) e pelo uso dos marcadores óxido crômico (OC) e lignina (LIG). Foram utilizados 24 animais, nove equinos, seis asininos e nove muares, em delineamento experimental inteiramente ao acaso, com nove tratamentos em esquema fatorial 3 x 3 (três espécies e três marcadores), com três repetiçöes para equinos e muares e duas para jumentos. O experimento teve duraçäo de 28 dias. A dieta era composta de feno de "Coast cross" picado (PB=7,8 por cento) e concentrado (PB=12,7 por cento) à base de milho desintegrado com sabugo, milho gräo, farelo de trigo, farelo de soja, calcário e fosfato bicálcio. A relaçäo volumoso/concentrado foi de 1:1, fornecida no equivalente a 2 por cento do peso vivo em MS/dia, de acordo com o seguinte esquema de arraçoamento: A=7h e 13h (volumoso), 9h e 15h (concentrado);B=7h e 15h (volumoso), 11h e 19h (concentrado); C=7h (concentrado total e 1/3 do volumoso), 15h (2/3 do volumoso). Näo foram encontradas diferenças significativas entre os coeficientes de digestibilidade da HCEL (67,12 e 63,55) e CEL (51,06 e 46,58) obtidos pelos indicadores CT, LIG, mas diferentes pelo indicador OC (58,34 e 38,41). Os coeficientes de digestiblidade da PB (71,01, 67,78 e 63,12), da MS (64,15, 59,03 e 52,99), da FDN (51,20, 46,53 e 38,61), da EB (64,60, 60,77 e 54,94) e da FDA (33,23, 66,03 E 18,84) obtidos respectivamente pela CT, LIG e OC diferiram entre si